Such devices are known e.g. through company memo Zahnradfabrik Friedrichshafen ZF-B- Blocking Synchronization F 42290/R2964-367, the German Patent Nos. 14 50 825 and 29 15 965, and the German Patent document No. 32 21 712.
All these devices have in common that blocking surfaces which are provided on the synchronizing ring or the sliding sleeve prevent full engagement between synchronizing body and gear via the sliding sleeve, until synchronization is attained by means of conically shaped friction surfaces. On the one hand, the friction surfaces are provided on at least one synchronizing ring which is rotatably connected to the synchronizing body with circumferential play; on the other hand they cooperate with the gear which is to be clutched in, or a coupling body on said gear. Such blocking synchronization devices which are applied to modern gear shifting drives, lead to significant simplifications in the shifting of gears, and are built as required especially for gear shifts for heavy duty vehicles, also with amplifying means, for synchronization, see German Patent document No. 32 21 712. All these lack synchronization devices have the common drawback due to the necessary actuating clearance between friction surfaces which are constructed with an angle of more than 10.degree., they have large axial dimension. If there is more than one friction array in a shift clutch, or if in a transmission several shift clutches are arranged next to one another in axial direction, then the overall length is significantly affected. In this connection, due to the friction couples, energy losses will arise. A further disadvantage of a lock synchronization containing friction cones is their high susceptibility to radial displacement within the cones.